Spots on ceiling after painting

Old 12-26-10, 06:03 PM
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Spots on ceiling after painting

There are some spots on my ceiling. I figured they were water spots, but did not know for sure because my attic seems dry. I painted over them and they re-appear. Again checked my attic and seems dry. Do I have to treat those spots with something before I paint over them to stop them from coming through again? Links to pictures below.
Old 12-26-10, 09:10 PM
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I saw these stain-blocker primers on this website:


"A general purpose, solvent-based acrylic stain blocking primer. It blocks nicotine or old humidity stains, fireplace soot and fire stains, distempers and lime. Easy to sandpaper. It can be used as an emulsion (latex) and acrylic paints undercoat on walls, and as a topcoat for ceiling painting."


A white acrylic undercoat that seals, covers and can be colored at the same color of the final coat


A white flat-finish acrylic waterborne sealing undercoat, within the KRAFT MIX System, which renders the maximum number of colors of the index, reducing thus the need for multiple coatings of the final cover paint. Suitable for interior and exterior use, it is almost odorless, user and environmental friendly.

It is applied as a sealing undercoat of latex and acrylic paints on surfaces coated with water-based or solvent-based paints, or new properly prepared surfaces such as putty, gypsum boards, cement boards and concrete. It is a superior covering undercoat that acts as a barrier to dry stains from nicotine, smoke, old humidity, pens, marker pens, coffee, and juice and blocks them from moving to the final coating. "

The first one is solvent based so its safer to use on a well ventilated area due to the fumes. I am not sure how these work exactly but they are supposed to be blocking stains from reappearing on the surface after painting.
Are you sure its just some stain that was allready there or are they new stains that are appearing for some reason?
Old 12-27-10, 03:53 AM
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Those look like water stains so they will need a primer. Most any solvent based primer will work although a stain hiding primer is best. I wouldn't bother trying to use a water based primer as they seldom seal stains long term.
Old 12-27-10, 05:17 AM
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Yep, you need a sealing primer to keep these from bleeding through the paint
Old 12-28-10, 09:55 PM
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What actually happens when a stain "bleeds through" a primer or paint is that the staining material has dissolved in the thinner the paint uses, and has diffused through the wet primer or paint film to discolour the surface of that primer or paint.

(For example, most red, yellow and brown woods like cedar, redwood and southern yellow pine, have lots of tannins in them that give them their distinctive colour. Tannins are highly soluble in water. So, if you paint over southern yellow pine with a latex primer, you'll often find that the primer has brown stains on it when it dries. That's because the tannins in the wood dissolved in the water in the primer and diffused through the thickness of the primer film to discolour it's surface.)

So, whenever you encounter a stain that's likely to be caused by water, then priming over that stain with an oil based primer will generally block the stain. And, vice versa.

On a really cold evening, have a bath or shower, turn on the bathroom fan and go up into your attic. Check to see if there's any place where water condensate forming inside the bathroom (or kitchen ceiling fan vent piping could be leaking out onto your ceiling.

Also, while in the attic on a really cold day, look for frost forming anywhere on your roof rafters or on the underside of the roof sheathing. It's normal for warm moist air to escape from your house and get up into your attic. And, on a cold winter night, it's normal for that moisture to form dew or frost on the coldest surfaces in your attic, which will be the roof rafters or roof sheathing. But, if you have sufficient ventilation in your attic, that dew or frost will evaporate or sublimate in a few days, leaving the attic dry again. It's when you don't have sufficient attic ventilation that the frost accumulates and stays until the warmer weather melts it in spring.

The thing you have to watch out for in attic ventilation isn't just that the melt water could form water marks on your ceiling. It's the fact that insulation works by keeping air stagnant, and so wet insulation takes forever to dry out. And, since your ceiling joists are exposed to that wet insulation, that's just the kind of situation that can promote wood rot in those ceiling joists. And, to top it all off, the vapour barrier between the ceiling joists and the ceiling drywall keeps the ceiling drywall dryer than it otherwise would be, and that makes the problem look smaller than it very well might be.

So, the first thing I'd do is get above those water spots on your ceiling, and move the ceiling insulation away to see if there's any wood rot on any ceiling joists above those water marks.
Old 01-03-11, 05:01 PM
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I bought some stain sealing spray primer and it worked great. It sprays straight up. I have gone into the attic twice over the past few winters and all seemed well. I'll go up there again sometime after I've ran the shower and exaust fan. Thanks, -Troy

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